1. Field of the Invention
The present invention relates to a sheet stacking/aligning apparatus having a sheet rear end aligning member for pushing and aligning the rear end of a sheet.
2. Description of the Related Art
In the image forming apparatus of the related art such as a printer, a copying machine or a printer, as shown in FIG. 8, sheets S having images formed in an image forming apparatus body 300 are temporarily stacked on a handling tray 140 in an image forming apparatus body 100, in which the sheets S are subjected to a handling operation such as to a aligning operation or a stapling operation. After this, the sheet bundle of the handled sheets is discharged by bundle discharge means.
The discharged sheet bundle is stacked on a stack tray 400 having a sloped stack face, and the sheets S discharged in the bundle move on the sloped stack face of the stack tray 400 by their own weights and are aligned at their rear ends on a rear end aligning wall 401. The number of stacked sheets depends on the vertical running stroke of the stack tray 400. On the other hand, the stack tray 400 having the sloped stack face needs a height for the slope. The sheet handling apparatus 100 mounted in the image forming apparatus, as shown in FIG. 8, is restricted in its height so that it cannot have a sufficient number of stacks.
In case the bundle is to be discharged to a horizontal tray, on the other hand, there has been known a technique, in which the sheet bundle is conveyed and stacked by the bundle discharge means such as a gripper to and on a stack tray having a horizontal stack face. If the gripper technique is mounted as the bundle discharge means, however, its complicated mechanism enlarges the size of the entire image forming apparatus and raises the cost.
In order to solve these problems, there has been a sheet handling apparatus 1, which is provided with a sheet stacking/aligning apparatus for stacking a sheet bundle on a generally horizontal stack tray 4 by turning a rear end aligning wall 70, as shown in FIG. 9 and FIGS. 10A to 10D. The sheet stacking/aligning apparatus: conveys the sheet bundle till the rear end of the sheet bundle reaches the upper end of the rear end aligning wall 70 (FIG. 10B); turns and inclines the rear end aligning wall 70 with a cam 72 to bring the rear end of the sheet bundle into abutment against the side end of the rear end aligning wall 70 (FIG. 10C); and then stacks the sheet bundle on the gently inclined stack tray 4 (FIG. 10D) while turning the rear end aligning wall 70 in a returning direction to push the rear end of the sheet bundle with the side end of the rear end aligning wall 70 thereby to align the sheet bundle in the conveyance direction. As a result, the displacement at the front end and rear end in the sheet bundle conveyance direction can be prevented to improve the stack alignment of the sheet bundle on the stack tray 4 and to spare the space.
In case a sheet bundle curled upward is to be stacked, as shown in FIG. 11, however, the sheet stacking/aligning apparatus of the related art has a problem that the stack height is reduced in the extent of the curl (i.e., the height L in FIG. 11).
Even without the curl, moreover, the thickness of the sheet bundle is enlarged by the air layers between the sheets in the sheet bundle thereby to reduce the number of stacked sheets. If the number of stacked sheets is to be retained, on the other hand, there arises a problem that the apparatus is accordingly enlarged to retain the vertical working stroke of the tray.
Moreover, the rear end of the sheet bundle, which is discharged to ride on a driven roller 71 due to the curl, collides against the sheet bundle to be next handled, and the stack fault may be caused by pushing the sheet bundle in the discharge direction.
At the time of rocking the rear end aligning wall 70, on the other hand, the sheet bundle leans against the rear end aligning wall 70 and cannot be aligned thereby to cause the stack fault.